linux-kernel - Re: Bug on 2.6.26 - x86 VIA Nehemiah CentaurHauls processor cannot boot

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Message-ID: <488B6E7B.9040908@zytor.com>
Date:	Sat, 26 Jul 2008 14:35:39 -0400
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Ingo Molnar <mingo@...e.hu>,
	"Luis R. Rodriguez" <mcgrof@...il.com>,
	linux kernel <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...nel.org>,
	Ivan Seskar <Seskar@...lab.rutgers.edu>,
	jfm3 <jfm3@...lab.rutgers.edu>, Sujith <m.sujith@...il.com>
Subject: Re: Bug on 2.6.26 - x86 VIA Nehemiah CentaurHauls processor cannot
 boot

Andi Kleen wrote:
> 
> This was originally supposed to be handled in the early real mode
> head.S code. That is why I put the CPUID checking code in there
> to error out early when you can still print to the console
> using the BIOS functions.
> 
> I suspect this regressed when that code was moved to C, because
> now the C compiler generates CMOV early.
> 
> How about always building the real mode C code with -march=i386?
> It is not performance critical so that is ok.
> 

The real mode code *is* compiled with -march=i386, and in the CMOV case 
it will err out with a legible message.

The issue isn't CMOV at all, it's with long NOPs, which don't have a 
CPUID bit -- they're supposed to be supported if family >= 6, but some 
VIA chips violate that condition.

	-hpa
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